1. Field of the Invention
The invention relates to tough, crystalline aromatic polyetherketones, processes for making them and monomers used in their manufacture. The polyetherketones are derived from monomers which provide the repeating polymer unit
--(--O--Ph--CO--Ph--CO--Ph--).sub..gtoreq.2 -- in the polymer chain.
2. Description of the Prior Art
Polyetherketones are a known class of tough, crystalline engineering plastics that have received renewed attention in recent years because of a need for crystalline thermoplastics having high crystalline melting temperatures (T.sub.m), high second order (glass) transition temperatures (T.sub.g), substantial inertness to most solvents and excellent moisture stability. These polymers have demonstrated good electrical insulating properties, such as for high service temperature wire insulation, and are finding uses in glass fiber, aromatic polyamide fiber or carbon fiber reinforced composites. Two polyetherketones have been commercialized to date. The first commercial polyetherketone was Stilan.TM. (made by Raychem Company) having the repeating unit structure 'Ph--O--Ph--CO--("PEK") wherein "Ph" is the 1,4-phenylene unit. Its commercial manufacture ceased in about the mid-1970s. More recently, Imperial Chemicals Industries PLC ("ICI") commercialized a polyetherketone of the repeating unit formula EQU --O--Ph--O--Ph--CO--Ph--
("Peek") called Victrex.TM. PEEK and has obtained patents thereon, see U.S. Pat. No. 4,320,224, patented Mar. 16, 1982 and European Pat. No. 0 001 879, published Mar. 24, 1982.
As used in this specification, the ether unit will be characterized as E, the ketone (carbonyl) unit will be characterized as K, the fact that combinations of E's and K's are part of a repeating polymeric unit will be designated by a P prefix, and the existance of 1,4-phenylene separating each E and K is to be inferred.
The broadest definition of polyetherketones includes a vast array of unit structures therein, including ether sulfone and biphenylene units. However, from a practical standpoint, the commercial polyetherketones are made up of simple repeat units because even the simplest polyetherketones are very expensive to make. The high costs of the polyetherketones stem from the high processing cost to keep the polymerizing, highly crystalline polymer in solution until the desired molecular weight is achieved (thereby avoiding crystallization out of solution prematurely) and/or the reliance on the use of expensive fluorine containing monomeric starting materials. This is amplified below.
It is recognized that polyetherketones can be made by two procedures: the electrophilic aromatic displacement or substitution reaction and the nucleophilic aromatic displacement or substitution reaction. The former was used to make Stilan.TM. and is demonstrated in Dahl, U.S. Pat. No. 3,953,400, patented Apr. 27, 1976, and Dahl U.S. Pat. No. 3,956,240, patented May 11, 1976. Dahl had demonstrated that in the electrophilic reaction, premature crystallization out of solution could be aborted by polymerizing in HF as the solvent. The reactant used for the reaction was the relatively cheaper monocarboxylic acid chloride of diphenylether, i.e.,
Ph--O--Ph--COCl ("Ph--" is phenyl). The catalyst was a Friedel-Crafts catalyst such as boron trifluoride. Apparently, the corrosive nature of HF caused the cessation of the commercial operation by Raychem Company.
The nucleophilic displacement process for making polyetherketones is well characterized by Johnson et al., Journal of Polymer Science, Part A-1, vol. 5, pages 2375-2398, 1967. ICI adapted that process for making Victrex.TM. PEEK by the condensation reaction of hydroquinone with the expensive 4,4'-difluorobenzophenone. Premature crystallization was avoided by (a) the use of diphenyl sulphone as the solvent, and (b) advancing polymerization by temperature increase but always below the solvent's boiling point.
ICI's patented technology as it relates to wholly polyetherketones depends on the condensation of hydroquinone and 4,4'-difluorobenzophenone. The only difluorobenzenoid compound used in the examples of the ICI patent is 4,4'-difluorobenzophenone. The only bisphenol other than hydroquinone used in the examples of the ICI patent is 4,4-dihydroxybenzophenone. As a consequence, the polymers there illustrated are limited in the scope of their T.sub.m and T.sub.g ; the range of T.sub.m 's being 334.degree. C. to 345.degree. C., and T.sub.g 's being 140.degree. C. to 154.degree. C.
The ether to ketone molar ratio ("E/K ratio") of a polyetherketone composed of copolymeric ether and ketone units joined only by 1,4-phenylene units is a most significant factor in characterizing physical properties. It has been established that ordered or random polyetherketones of the same E/K ratio have the same T.sub.m and T.sub.g regardless of the ether and ketone arrangement. For example, each of the polyetherketones --0--Ph--CO--Ph--and --O--Ph--O--Ph--CO--Ph--CO--Ph--have the E/K ratio of 1 and they have the same T.sub.m and T.sub.g. As is the case with all of such polyetherketones of appropriate molecular weights, they have comparable service properties ("service" in the sense of commercial uses). However, a demand has arisen for polyetherketones having T.sub.m s greater than that of PEEK, indeed, even greater than PEK. Because T.sub.g s track T.sub.m s in these polymers, higher T.sub.g s are a direct benefit of the higher T.sub.m s. Therefore, it would be most desirable to be able to make polyetherketones of a variety of E/K ratios, such as below that of PEEK or PEK, as needed, from a limited number of simple monomers beyond the scope of the prior art.
The polyetherketones that have been commercially manufactured, namely ICI's Victrex.TM. PEEK and Raychem's Stilan.TM., are/were made from a minimum of starting materials. Victrex.TM. PEEK is made from hydroquinone and 4,4'-difluorobenzophenone and Stilan.TM. was made from p-phenoxybenzoylchloride. The starting materials in both cases are expensive; however, because of the cost of making difluorobenzophenone, Stilan.TM. on a raw-material basis is perceived to be the cheaper polymer. Because Stilan.TM. has the lower E/K ratio of 1 as contrasted to 2 for PEEK, Stilan.TM. has a higher T.sub.m and T.sub.g, making it a superior performing polymer. One monomer is used in making Stilan.TM. and that is desirable from a cost/production standpoint. Because hydroquinone is a commercially available chemical, only one chemical has to be specially made for making PEEK, namely, 4,4'-difluorobenzophenone. The commercial availability of that monomer based on a broader consumption than PEEK manufacture would significantly lower the cost of PEEK. These cost factors are important to the eventual consumption and utility of the polymers. In order to produce polyetherketones having higher, intermediate or lower E/K ratios than PEK and PEEK, it is necessary to make expensive monomers, other than those cited above, or to make and introduce new monomers to the monomer compositions used to make PEK and PEEK.
However, the Friedel-Crafts process has already been established as a difficult one for making a commercially acceptable polyetherketone. Its operation to make a homopolymer has been shown by Raychem to be hazardous, thus to make a copolymer with a variance on structure to the same or different E/K ratio of the PEK polymer, by the same process, can be accurately termed a treacherous endeavor, subject to significant branching or crosslinking problems. The Friedel-Crafts process exploits lower cost monomers, and indeed, if it could be effectively practiced by directly reacting phosgene with aromatic ethers, the advantage in monomer cost over the nucleophilic route would be significant enough to eliminate the latter route as a potential competitor. However, such is not the case and the only existing commercial route to such polyetherketones is by the nucleophilic process.
U.S. Pat. No. 4,320,224 describes a number of monomers that can be used in making polyetherketones having an E/K ratio below 2. Specifically, they are the following:
A. Bisphenols
4,4'-dihydroxybenzophenone PA2 4,4'-dihydroxydiphenylsulphone PA2 2,2'-bis-(4-hydroxyphenyl)propane PA2 4,4'-dihydroxybiphenyl PA2 hydroquinone PA2 4,4'-dichlorodiphenylsulphone PA2 4,4'-difluorodiphenylsulphone PA2 4,4'-dichlorobenzophenone PA2 4,4'-difluorobenzophenone PA2 bis-4,4'-(4-chlorophenylsulphonyl)biphenyl PA2 bis-1,4-(4-chlorobenzoyl)benzene PA2 bis-1,4-(4-fluorobenzoyl)benzene PA2 4-chloro-4'-fluorobenzophenone PA2 4,4'-bis-(4-fluorobenzoyl)biphenyl PA2 4,4'-bis-(4-chlorobenzoyl)biphenyl PA2 (a.) HO--Ph--CO--Ph--CO--Ph--X PA2 (b.) HO--Ph--CO--Ph--CO--Ph--OH PA2 (c.) X--Ph--CO--Ph--CO--Ph--X. PA2 1. HO--Ph--O--Ph--OH PA2 2. HO--Ph--CO--Ph--OH PA2 3. HO--Ph--CO--Ph--CO--Ph--OH PA2 4. HO--Ph--CO--Ph--CO--Ph--CO--Ph--OH PA2 1. F--Ph--CO--Ph--CO--Ph--F PA2 2. F--Ph--CO--Ph--CO--Ph--CO--Ph--F PA2 3. F--Ph--CO--Ph--CO--Ph--CO--Ph--F
B. Dihalides
Of the listed bisphenols, only hydroquinone and 4,4'-dihydroxybenzophenone will generate a polyetherketone which is wholly ether, 1,4-phenylene and ketone units. Of the listed dihalides, only 4,4'-dichloro or difluoro or chlorofluoro benzophenone, or bis-1,4-(4-chloro or fluorobenzoyl)benzene will do the same. It is recognized that only a small proportion of the dihalide used can be the chloride variant without adversely affecting the properties of the polymer produced.
However, by selecting the three reactants
______________________________________ Bisphenol Dihalide ______________________________________ hydroquinone 4,4'-difluorobenzophenone bis-1,4-(4-fluorobenzoyl)benzene ______________________________________
one may generate polyetherketones having E/K ratios extending between 2 and 1, achieving the full range of T.sub.m 's and T.sub.g 's attending those ratios. However, U.S. Pat. No. 4,320,224 specifies that at least 50 mole % of the polymer must be made from 4,4'-difluorobenzophenone. However, that preference is not viewed to be a technical limitation, merely one made to attempt to differentiate for the purpose of patentability.
There is described herein polyetherketone compositions and a process which can (a) avoid infringing any of the prior art patents such as U.S. Pat. Nos. 3,953,400, 3,956,240 and 4,320,224, and their foreign counterparts; (b) provide physical properties which are at least equal to such prior art polyetherketones; and (c) be made or practiced by the use of monomers potentially less expensive than those of the prior art. The invention has the benefit of being capable of making random copolymers or block copolymers with special benefits in each case. In the case of block copolymers, the invention can generate polymers having higher rates of crystallization, higher T.sub.m s and higher T.sub.g s than comparable E/K ratio random or ordered copolymers. The invention allows the production of polyetherketones having E/K mole ratios from about 2 to as low as about 0.5.